The invention relates to a camshaft adjuster for an internal combustion engine.
Camshaft adjusters can be classified roughly as follows:
A. Phase adjusters with a control unit, that is, a functional unit, which engages in the mass flow or energy flow, which, for example, has a hydraulic, electric, or mechanical construction, and which rotates with gear elements of the camshaft adjuster.
B. Phase adjusters with a separate regulator, that is, a functional unit, in which the control parameter necessary for controlling the modulation of the control unit is derived from the regulator output parameter, and with a separate control unit. Here there are the following constructions:                a. Phase adjuster with a co-rotating actuator and a co-rotating control unit, for example, a speed increasing gearbox, whose adjustment shaft can be preset by a co-rotating hydraulic motor or centrifugal force motor and can be reset by means of a spring.        b. Phase adjuster with a co-rotating control unit and a stationary, motor-fixed actuator, for example, an electric motor or an electric or mechanical brake, see also DE 100 38 354 A1, DE 102 05 034 A1, EP 1 043 482 B1.        c. Phase adjuster with a direction-dependent combination of solutions according to a and b, for example, a motor-fixed brake, in which part of the braking power is used, for example, for shifting in the advanced direction, in order to tension a spring that can reset the brake after the brake is switched off, see also DE 102 24 446 A1, WO 03-098010, US 2003 0226634, DE 103 17 607 A1.        
For systems according to B.a. to B.c., actuators and control units are connected to each other by means of an adjustment shaft. The connection can be switchable or non-switchable, detachable or non-detachable, without backlash or with backlash, and flexible or stiff. Independent of the structural shape, the adjustment energy can be realized in the form of providing driving and/or braking power, as well as using loss power of the shaft system (e.g., friction) and/or inertial and/or centrifugal forces. Braking, preferably in the “retarded” adjustment direction, can also be realized under complete use or co-use of the frictional output of the camshaft. A camshaft adjuster can be equipped with or without mechanical limiting of the adjustment range. As the drive in a camshaft adjuster, one-stage or multiple-stage triple-shaft drives and/or multiple linkages or coupling gears can be used, for example, with a structural shape as a swashplate mechanism, eccentric drive, planetary gear drive, shaft drive, cam plate drive, multiple linkage or coupling drive, or combinations of the individual structures for a multiple-stage configuration.
While conventional, hydraulically activated camshaft adjusters or camshaft adjusters in a construction with vane cells, pivot vanes, or segmented vanes have the advantage that                The hydraulic medium can be fed into the camshaft adjuster at any point for control,        The hydraulic medium is fed into the camshaft adjuster via suitable flow channels,        The hydraulic medium—if necessary—can be diverted and        Suitable devices for controlling the hydraulic pressure can also be arranged eccentric from the camshaft adjuster,in conventional camshaft adjusters, in which the control movement is generated via an electric motor and a superposition drive, triple-shaft drive, or planetary gear drive (in the following superposition drive), see, e.g., DE 41 10 195 A1, the electric motor is typically arranged in front of the superposition drive aligned to the longitudinal axis of the camshaft and the superposition drive. For this reason, such camshaft adjusters with an electric control unit and a superposition drive are built axially larger than corresponding hydraulically actuated camshaft adjusters. Attaching an accessory unit, such as a vacuum pump, to the camshaft adjuster on the side of the superposition drive facing away from the camshaft is not possible, because the electric control unit is arranged in this installation space.        
From DE 37 37 602 A1 it is known to use a differential gear drive as the superposition drive, in which a drive is realized via a driving wheel in driving connection with the crankshaft and a driven part relative to the camshaft aligned with the longitudinal axis, while the feeding of the drive motion of the electric control unit is realized radially relative to the previously mentioned longitudinal axis.
From DE 102 60 546 A1, a hydraulic camshaft adjuster is known, to which a vacuum pump can be coupled on the side facing away from the camshaft aligned with the longitudinal axis.
DE 38 30 382 C1 discloses the drive of a planetary gear drive mounted axially in front of a superposition drive via an electric control unit, whose longitudinal axis is offset parallel to the longitudinal axis of the camshaft and the superposition drive.
The superposition drive known from U.S. Pat. No. 4,747,375 is constructed as a planetary gear drive, in which for a first construction the ring gear is driven by a servomotor, whose longitudinal axis is arranged parallel to the longitudinal axis of the camshaft, while the sun gear of the planetary gear is in drive connection with the crankshaft of the internal combustion engine and a driven part of the planetary gear relative to the camshaft is realized via the web. For an alternative construction, the drive is realized via the servomotor and the sun gear for aligned alignment of the servomotor relative to the longitudinal axis of the camshaft, while the crankshaft drives the ring gear for a driven part via the web of the planetary gear.
Finally, DE 103 52 255 A1 discloses a coupling of an electric control unit via a flexible shaft, a pneumatic motor, or a hydraulic motor, so that the control unit can be arranged at any point. Furthermore, the publication presents the proposal of arranging an electric control unit parallel to the camshaft and connecting a gear stage between the superposition drive and the electric control unit.